Diesel soot (any carbon in suspension ?) seems to be pretty abrasive stuff in spite of it's small size, where it's not supposed to cause wear per some theorys as it's smaller than the oil film thickness, much smaller. It supports other Cummins and DOE studies where they found that used oil was needed for wear testing as it casued a lot more wear than fresh oil. The anti-wear film degradation was interesting as in a severe state it could cause more wear than an oil without the additives.
http://www.oetg.at/website/wtc2001cd/html/abstracts-search.htm
M-27-13-450-MASUKO.pdf
ENGINE OIL AND ITS EFFECT ON THE ANTIWEAR PERFORMANCE - ZnDTP DEGRADATION AND CARBON SOOT CONTAMINATION
The antiwear performance of simulated used-engine-oil that contained degraded Zinc dialkyldithiophosphate (ZnDTP) was studied with and without carbon soot using a four-ball tribometer. By reacting with cumene hydroperoxide, sec-C6 ZnDTP degraded and produced many compounds containing both phosphorous and sulfur. The simulated used-oils were found to increase wear. It is considered to be due to corrosive wear by excess reaction of surfaces with sulfur in the degraded compounds. Carbon black was used as model carbon soot, that is another key substance of degraded engine oils especially in diesel engines, to study synergism of ZnDTP degradation and carbon soot contamination. Carbon black increased wear regardless of ZnDTP degradation and the acceleration was much larger in the degraded oils. The wear acceleration by carbon black was observed even when the antiwear film by ZnDTP was already formed on the surface. It was suggested that the wear acceleration by carbon black was abrasive.
http://www.oetg.at/website/wtc2001cd/html/abstracts-search.htm
M-27-13-450-MASUKO.pdf
ENGINE OIL AND ITS EFFECT ON THE ANTIWEAR PERFORMANCE - ZnDTP DEGRADATION AND CARBON SOOT CONTAMINATION
The antiwear performance of simulated used-engine-oil that contained degraded Zinc dialkyldithiophosphate (ZnDTP) was studied with and without carbon soot using a four-ball tribometer. By reacting with cumene hydroperoxide, sec-C6 ZnDTP degraded and produced many compounds containing both phosphorous and sulfur. The simulated used-oils were found to increase wear. It is considered to be due to corrosive wear by excess reaction of surfaces with sulfur in the degraded compounds. Carbon black was used as model carbon soot, that is another key substance of degraded engine oils especially in diesel engines, to study synergism of ZnDTP degradation and carbon soot contamination. Carbon black increased wear regardless of ZnDTP degradation and the acceleration was much larger in the degraded oils. The wear acceleration by carbon black was observed even when the antiwear film by ZnDTP was already formed on the surface. It was suggested that the wear acceleration by carbon black was abrasive.
